System and methods for electrosurgical treatment of obstructive sleep disorders

ABSTRACT

The present invention provides systems and methods for selectively applying electrical energy to a target location within the head and neck of a patient&#39;s body, particularly including tissue in the ear, nose and throat. The present invention includes a channeling technique in which small holes or channels are formed within tissue structures in the mouth, such as the tonsils, tongue, palate and uvula, and thermal energy is applied to the tissue surface immediately surrounding these holes or channels to cause thermal damage to the tissue surface, thereby stiffening the surrounding tissue structure. Applicant has discovered that such stiffening of certain tissue structures in the mouth and throat helps to prevent the tissue structure from obstructing the patient&#39;s upper airway during sleep.

RELATED APPLICATIONS

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 09/054,323, U.S. Pat. No. 6,063,079, U.S. patentapplication Ser. No. 09/083,526, U.S. Pat. No. 6,053,172, and U.S.patent application Ser. No. 09/136,079, U.S. Pat. No. 6,086,585, filedApr. 2, 1998, filed May 22, 1998 and Aug. 18, 1998, respectively, eachof which are continuation-in-parts of Ser. No. 08/990,374, filed Dec.15, 1997, which is a continuation-in-part of U.S. patent applicationSer. No. 08/485,219, U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995, thecomplete disclosures of which are incorporated herein by reference forall purposes.

The present invention is related to commonly assigned U.S. patentapplication Ser. No. 09/058,571, filed on Apr. 10, 1998 and U.S. patentapplication Ser. No. 09/074,020, filed on May 6, 1998, U.S. patentapplication Ser. No. 09/010,382, filed Jan. 21, 1998, and U.S. patentapplication Ser. No. 09/032,375, filed Feb. 27, 1998, U.S. patentapplication Ser. No. 08/977,845, filed on Nov. 25, 1997, U.S. patentapplication Ser. No. 08/942,580, filed on Oct. 2, 1997, U.S. patentapplication Ser. No. 09/026,851, filed Feb. 20, 1998, U.S. applicationSer. No. 08/753,227, filed on Nov. 22, 1996, U.S. application Ser. No.08/687,792, filed on Jul. 18, 1996, and PCT International Application,U.S. National Phase Ser. No. PCT/US94/05168, filed on May 10, 1994, nowU.S. Pat. No. 5,697,909, which was a continuation-in-part of U.S. patentapplication Ser. No. 08/059,681, filed on May 10, 1993, which was acontinuation-in-part of U.S. patent application Ser. No. 07/958,977,filed on Oct. 9, 1992 which was a continuation-in-part of U.S. patentapplication Ser. No. 07/817,575, filed on Jan. 7, 1992, the completedisclosures of which are incorporated herein by reference for allpurposes. The present invention is also related to commonly assignedU.S. Pat. No. 5,697,882, filed Nov. 22, 1995, the complete disclosure ofwhich is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the head andneck, such as the ear, nose and throat. The present invention isparticularly suited for treating obstructive sleep disorders, such assleep-apnea, snoring and the like.

Sleep-apnea syndrome is a medical condition characterized by daytimehypersomnolence, intellectual deterioration, cardiac arrhythmias,snoring and thrashing during sleep. This syndrome is typically dividedinto two types. One type, termed "central sleep apnea syndrome", ischaracterized by repeated loss of respiratory effort. The second type,termed obstructive sleep apnea syndrome, is characterized by repeatedapneic episodes during sleep resulting from obstruction of the patient'supper airway.

Treatment for sleep apnea has included various medical, surgical andphysical measures. Medical measures include the use of medications andthe avoidance of central nervous system depressants, such as sedativesor alcohol. These measures are sometimes helpful, but rarely completelyeffective. Physical measures have included weight loss, openingnasopharygeal airways, nasal CPAP and various tongue retaining devicesused nocturnally. These measures are cumbersome, uncomfortable anddifficult to use for prolonged periods of time. In particular, CPAPdevices, which act essentially as a pneumatic "splint" to the airway toalleviate the obstruction, must be used for the entire patient'slifetime, and typically requires close to 100% usage of the device whilesleeping and napping. These factors result in limited patient compliancewith CPAP devices, reducing the effectiveness of the therapy.

Surgical interventions have included uvulopalatopharyngoplasty (UPPP),laser-assisted uvuloplasty procedures (LAUP), tonsillectomy, surgery tocorrect severe retrognathia and tracheostomy. The LAUP proceduresinvolve the use a CO₂ laser to excise and vaporize excess tissue in theregion of the palate and uvula. In UPPP procedures, a scalpel orconventional electrocautery device is typically employed to removeportions of the uvula, palate, pharynx and/or tonsils. While theseprocedures are effective, the risk of surgery in some patients is oftenprohibitive. In addition, UPPP and LAUP procedures performed withconventional electrocautery or laser devices typically generate extremepost-operative pain which may be unacceptable to the patient.

Recently, RF energy has been used to selectively destroy portions of thetongue and soft palate to treat air passage disorders, such as sleepapnea. This procedure, which was developed by Somnus MedicalTechnologies of Sunnyvale, Calif., involves the use of a monopolarelectrode that directs RF current into the target tissue to desiccate ordestroy submucosal tissue in the patient's mouth. Of course, suchmonopolar devices suffer from the disadvantage that the electric currentwill flow through undefined paths in the patient's body, therebyincreasing the risk of unwanted electrical stimulation to portions ofthe patient's body. In addition, since the defined path through thepatient's body has a relatively high impedance (because of the largedistance or resistivity of the patient's body), large voltagedifferences must typically be applied between the return and activeelectrodes in order to generate a current suitable for ablation orcutting of the target tissue. This current, however, may inadvertentlyflow along body paths having less impedance than the defined electricalpath, which will substantially increase the current flowing throughthese paths, possibly causing damage to or destroying surrounding tissueor neighboring peripheral nerves.

Another disadvantage of conventional RF devices, such as the Somnusmonopolar electrode, is that these devices typically operate by creatinga voltage difference between the active electrode and the target tissue,causing an electrical arc to form across the physical gap between theelectrode and tissue. At the point of contact of the electric arcs withtissue, rapid tissue heating occurs due to high current density betweenthe electrode and tissue. This high current density causes cellularfluids to rapidly vaporize into steam, thereby producing a "cuttingeffect" along the pathway of localized tissue heating. Thus, the tissueis parted along the pathway of evaporated cellular fluid, inducingundesirable collateral tissue damage in regions surrounding the targettissue site. This collateral tissue damage often causes indiscriminatedestruction of tissue, resulting in the loss of the proper function ofthe tissue. In addition, the device does not remove any tissue directly,but rather depends on destroying a zone of tissue and allowing the bodyto eventually remove the destroyed tissue.

Yet another disadvantage with the Somnus technology is that theprocedure typically takes a long time, often requiring the electricalenergy to be applied to the submucosal tissue for a period of longerthan a minute. This can be quite uncomfortable to the patient, who istypically awake during the procedure.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures in the head andneck of a patient's body, such as tissue within the ear, nose andthroat. The systems and methods of the present invention areparticularly useful for treating obstructive sleep disorders, such assnoring or sleep apnea. The present invention includes a channelingtechnique in which small holes or channels are formed within tissuestructures in the mouth, such as the tonsils, tongue, palate and uvula,and thermal energy is applied to the tissue surface immediatelysurrounding these holes or channels to cause thermal damage to thetissue surface, thereby stiffening the surrounding tissue structure.Applicant has discovered that such stiffening of certain tissuestructures in the mouth and throat helps to prevent the tissue structurefrom obstructing the patient's upper airway during sleep.

Methods of the present invention include introducing one or more activeelectrode(s) into the patient's mouth, and positioning the activeelectrode(s) adjacent the target tissue, e.g., selected portions of thetongue, tonsils, soft palate tissues (e.g., the uvula and pharynx), hardtissue or other mucosal tissue. High frequency voltage is appliedbetween the active electrode(s) and one or more return electrode(s) tovolumetrically remove or ablate at least a portion of the target tissue,and the active electrode(s) are advanced through the space left by theablated tissue to form a channel, hole, divot or other space in thetarget tissue. The active electrode(s) are then removed from thechannel, and other channels or holes may be formed at suitable locationsin the patient's mouth or throat. In preferred embodiments, highfrequency voltage is applied to the active electrode(s) as they areremoved from the hole or channel. The high frequency voltage is belowthe threshold for ablation of tissue to effect hemostasis of severedblood vessels within the tissue surface surrounding the hole. Inaddition, the high frequency voltage effects a controlled depth ofthermal heating of the tissue surrounding the hole to thermally damageat least the surface of this tissue without destroying or otherwisedebulking the underlying tissue. This thermal damage stiffens the tissuestructure, thereby reducing obstructions to the patient's air passages.

In a specific configuration, electrically conductive media, such asisotonic saline or an electrically conductive gel, is delivered to thetarget site within the mouth to substantially surround the activeelectrode(s) with the media. The media may be delivered through aninstrument to the specific target site, or the entire target region maybe filled with conductive media such that the electrode terminal(s) aresubmerged during the procedure. Alternatively, the distal end of theinstrument may be dipped or otherwise applied to the conductive mediaprior to introduction into the patient's mouth. In all of theseembodiments, the electrically conductive media is applied or deliveredsuch that it provides a current flow path between the active and returnelectrode(s). In other embodiments, the intracellular conductive fluidin the patient's tissue may be used as a substitute for, or as asupplement to, the electrically conductive media that is applied ordelivered to the target site. For example, in some embodiments, theinstrument is dipped into conductive media to provide a sufficientamount of fluid to initiate the requisite conditions for ablation. Afterinitiation, the conductive fluid already present in the patient's tissueis used to sustain these conditions.

In the representative embodiments, the active electrode(s) are advancedinto the target tissue in the ablation mode, where the high frequencyvoltage is sufficient to ablate or remove the target tissue throughmolecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the electrodeterminal(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel, saline and/or intracellular fluid) between the electrodeterminal(s) and the tissue. Within the vaporized fluid, a ionized plasmais formed and charged particles (e.g., electrons) are acceleratedtowards the tissue to cause the molecular breakdown or disintegration ofseveral cell layers of the tissue. This molecular dissociation isaccompanied by the volumetric removal of the tissue. The short range ofthe accelerated charged particles within the plasma layer confines themolecular dissociation process to the surface layer to minimize damageand necrosis to the underlying tissue. This process can be preciselycontrolled to effect the volumetric removal of tissue as thin as 10 to150 microns with minimal heating of, or damage to, surrounding orunderlying tissue structures. A more complete description of thisphenomena is described in commonly assigned U.S. Pat. No. 5,697,882 thecomplete disclosure of which is incorporated herein by reference.

The active electrode(s) are usually removed from the holes or channelsin the subablation or thermal heating mode, where the high frequencyvoltage is below the threshold for ablation as described above, butsufficient to coagulate severed blood vessels and to effect thermaldamage to at least the surface tissue surrounding the holes. In someembodiments, the active electrode(s) are immediately removed from theholes after being placed into the subablation mode. In otherembodiments, the physician may desire to control the rate of removal ofthe active electrode(s) and/or leave the active electrode(s) in the holefor a period of time, e.g., on the order of about 1 to 5 seconds, in thesubablation mode to increase the depth of thermal damage to the tissue.

In one method, high frequency voltage is applied, in the ablation mode,between one or more active electrode(s) and a return electrode spacedaxially from the active electrode(s), and the active electrode(s) areadvanced into the tissue to form a hole or channel as described above.High frequency voltage is then applied between the return electrode andone or more third electrode(s), in the thermal heating mode, as theelectrosurgical instrument is removed from the hole. In one embodiment,the third electrode is a dispersive return pad on the external surfaceof the skin. In this embodiment, the thermal heating mode is a monopolarmode, in which current flows from the return electrode, through thepatient's body, to the return pad. In other embodiments, the thirdelectrode(s) are located on the electrosurgical instrument and thethermal heating mode is bipolar. In all of the embodiments, the thirdelectrode(s) are designed to increase the depth of current penetrationin the tissue over the ablation mode so as to increase the thermaldamage.

In one method, an electrosurgical instrument having an electrodeassembly is dipped into electrically conductive fluid such that theconductive fluid is located around and between both active and returnelectrodes in the electrode assembly. The instrument is then introducedinto the patient's mouth to the back of the tongue, and a plurality ofholes are formed across the base of the tongue as described above. Theinstrument is removed from each hole in the thermal heating mode tocreate thermal damage and to coagulate blood vessels. Typically, theinstrument will be dipped into the conductive fluid after being removedfrom each hole to ensure that sufficient conductive fluid exists forplasma formation and to conduct electric current between the active andreturn electrodes. This procedure stiffens the base of the tongue, whichinhibits the tongue from obstructing breathing as the patient sleeps.

Systems according to the present invention generally include anelectrosurgical instrument having a shaft with proximal and distal ends,an electrode assembly at the distal end and one or more connectorscoupling the electrode assembly to a source of high frequency electricalenergy. The electrode assembly includes one or more active electrode(s)configured for tissue ablation, and one or more return electrode(s)typically spaced from the active electrode(s) on the instrument shaft.In an exemplary embodiment, the return electrode(s) are spaced asufficient distance from the electrode terminal(s) to substantiallyavoid or minimize current shorting therebetween and to shield the returnelectrode(s) from tissue at the target site. The system further includesa third electrode, and a switch or other mechanism for moving theelectrode assembly between an ablation mode where the third electrode isdeactivated and the active and return electrodes receive a highfrequency voltage therebetween, and a thermal heating mode, where theactive electrode(s) are deactivated and the return and third electrodesreceive a high frequency voltage therebetween.

In one embodiment, the third electrode comprises a dispersive return padconfigured for attachment to an external skin surface of the patient. Inthis embodiment, the system functions as a monopolar electrosurgerydevice in the thermal heating mode and a bipolar or unipolarelectrosurgery device in the ablation mode. In another embodiment, thethird electrode is located on the instrument shaft and spaced axiallyfrom the active and return electrodes. In a specific configuration, thethird electrode comprises a pair of annular conductive bands on theinstrument shaft on either side of the return electrode. In thisembodiment, current flows from the return electrode to the twoconductive bands in the thermal heating mode.

The apparatus may further include a fluid delivery element fordelivering electrically conducting fluid to the electrode terminal(s)and the target site. The fluid delivery element may be located on theinstrument, e.g., a fluid lumen or tube, or it may be part of a separateinstrument. Alternatively, an electrically conducting gel or spray, suchas a saline electrolyte or other conductive gel, may be applied to theelectrode assembly or the target site. In this embodiment, the apparatusmay not have a fluid delivery element. In both embodiments, theelectrically conducting fluid will preferably generate a current flowpath between the electrode terminal(s) and the return electrode(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 3 is an end view of the probe of FIG. 2

FIG. 4 is a cross sectional view of the electrosurgical probe of FIG. 1;

FIG. 5 is an exploded view of a proximal portion of the electrosurgicalprobe;

FIG. 6 is perspective and end views, respectively, of an alternativeelectrosurgical probe incorporating an inner fluid lumen;

FIGS. 7A-7C are cross-sectional views of the distal portions of threedifferent embodiments of an electrosurgical probe according to thepresent invention;

FIGS. 8A and 8B are cross-sectional and end views, respectively, of yetanother electrosurgical probe incorporating flattened electrodeterminals;

FIG. 9 illustrates an electrosurgical probe with a 90° distal bend and alateral fluid lumen;

FIG. 10 illustrates an electrosurgical system with a separate fluiddelivery instrument according to the present invention;

FIGS. 11A and 11B illustrate a detailed view of the ablation of tissueaccording to the present invention;

FIGS. 12A-12C illustrate three embodiments of electrosurgical probesspecifically designed for treating obstructive sleep disorders;

FIG. 13 illustrates an alternative embodiment of an electrosurgicalprobe for treating obstructive sleep disorders;

FIG. 14 illustrates an electrosurgical system incorporating a dispersivereturn pad for monopolar and/or bipolar operations;

FIG. 15 illustrates a catheter system for electrosurgical treatment ofbody structures within the head and neck according to the presentinvention;

FIG. 16 is a cross-section view of a working end of a catheter accordingto one embodiment of the present invention;

FIG. 17A is a cross-section view of a working end of a catheteraccording to a second embodiment of the present invention;

FIG. 17B is an end view of the catheter of FIG. 17A;

FIG. 18 illustrates a procedure for treating obstructive sleepdisorders, such as sleep apnea, according to the present invention;

FIG. 19 is a top view of the tongue, illustrates a plurality of channelsnear the back of the tongue, generated with the techniques of thepresent invention;

FIG. 20 is a side view of the tongue, illustrating a single channel; and

FIG. 21 is a detailed view of a single channel generated with thetechniques of the present invention.

FIGS. 22-24 illustrate a high frequent power supply.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue in the head and neck, such as theear, mouth, pharynx, larynx, esophagus, nasal cavity and sinuses. Theseprocedures may be performed through the mouth or nose using speculae orgags, or using endoscopic techniques, such as functional endoscopicsinus surgery (FESS). These procedures may include the removal ofswollen tissue, chronically-diseased inflamed and hypertrophic mucuslinings, polyps and/or neoplasms from the various anatomical sinuses ofthe skull, the turbinates and nasal passages, in the tonsil, adenoid,epi-glottic and supra-glottic regions, and salivary glands, submucusresection of the nasal septum, excision of diseased tissue, tracheabroncheal strictures and the like. In other procedures, the presentinvention may be useful for collagen shrinkage, ablation and/orhemostasis in procedures for treating snoring and obstructive sleepapnea (e.g., soft palate, such as the uvula, or tongue/pharynxstiffening, and midline glossectomies), for gross tissue removal, suchas tonsillectomies, adenoidectomies, tracheal stenosis and vocal cordpolyps and lesions, or for the resection or ablation of facial tumors ortumors within the mouth and pharynx, such as glossectomies,laryngectomies, acoustic neuroma procedures and nasal ablationprocedures. In addition, the present invention is useful for procedureswithin the ear, such as stapedotomies, myringotomies, tympanostomies orthe like.

The present invention is particularly useful for treating snoring andobstructive sleep apnea by creating channels within the tongue, tonsils,palate, or uvula, to stiffen the tissue within these structures. Forconvenience, the remaining disclosure will be directed specifically tothe treatment of obstructive sleep disorders, but it will be appreciatedthat the system and method can be applied equally well to proceduresinvolving other tissues of the body, as well as to other proceduresincluding open procedures, intravascular procedures, urology,laparascopy, arthroscopy, thoracoscopy or other cardiac procedures,cosmetic surgery, orthopedics, gynecology, otorhinolaryngology, spinaland neurologic procedures, oncology and the like.

In one aspect of the invention, the tissue is volumetrically removed orablated to form holes, channels, divots or other spaces within the bodystructure. In this procedure, a high frequency voltage difference isapplied between one or more electrode terminal(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue. The high electric field intensities adjacent theelectrode terminal(s) lead to electric field induced molecular breakdownof target tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds.This molecular disintegration completely removes the tissue structure,as opposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue, as is typically the case withelectrosurgical desiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the electrode terminal(s) inthe region between the distal tip of the electrode terminal(s) and thetarget tissue. The electrically conductive fluid may be a liquid or gas,such as isotonic saline, blood or intracellular fluid, delivered to, oralready present at, the target site, or a viscous fluid, such as a gel,applied to the target site. Since the vapor layer or vaporized regionhas a relatively high electrical impedance, it increases the voltagedifferential between the electrode terminal tip and the tissue andcauses ionization within the vapor layer due to the presence of anionizable species (e.g., sodium when isotonic saline is the electricallyconducting fluid). This ionization, under the conditions describedherein, induces the discharge of energetic electrons and photons fromthe vapor layer and to the surface of the target tissue. This energy maybe in the form of energetic photons (e.g., ultraviolet radiation),energetic particles (e.g., electrons or ions) or a combination thereof.A more detailed description of this phenomena, termed Coblation™ can befound in commonly assigned U.S. Pat. No. 5,697,882 the completedisclosure of which is incorporated herein by reference.

Applicant believes that the principle mechanism of tissue removal in theCoblation™ mechanism of the present invention is energetic electrons orions that have been energized in a plasma adjacent to the electrodeterminal(s). When a liquid is heated enough that atoms vaporize off thesurface faster than they recondense, a gas is formed. When the gas isheated enough that the atoms collide with each other and knock theirelectrons off in the process, an ionized gas or plasma is formed (theso-called "fourth state of matter"). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

Plasmas may be formed by heating a small of gas and ionizing the gas bydriving an electric current through it, or by shining radio waves intothe gas. Generally, these methods of plasma formation give energy tofree electrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

In some embodiments, the present invention applies high frequency (RF)electrical energy in an electrically conducting media environment toremove (i.e., resect, cut or ablate) a tissue structure and to sealtransected vessels within the region of the target tissue. The presentinvention may also be useful for sealing larger arterial vessels, e.g.,on the order of about 1 mm in diameter. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an electrode terminal sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anelectrode terminal (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical instrument is provided having one ormore coagulation electrode(s) configured for sealing a severed vessel,such as an arterial vessel, and one or more electrode terminalsconfigured for either contracting the collagen fibers within the tissueor removing (ablating) the tissue, e.g., by applying sufficient energyto the tissue to effect molecular dissociation. In the latterembodiments, the coagulation electrode(s) may be configured such that asingle voltage can be applied to coagulate with the coagulationelectrode(s), and to ablate with the electrode terminal(s). In otherembodiments, the power supply is combined with the coagulationinstrument such that the coagulation electrode is used when the powersupply is in the coagulation mode (low voltage), and the electrodeterminal(s) are used when the power supply is in the ablation mode(higher voltage).

In one method of the present invention, one or more electrode terminalsare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the electrode terminals and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

In some embodiments of the present invention, the tissue is damaged in athermal heating mode to create necrosed or scarred tissue at the tissuesurface. The high frequency voltage in the thermal heating mode is belowthe threshold of ablation as described above, but sufficient to causesome thermal damage to the tissue immediately surrounding the electrodeswithout vaporizing or otherwise debulking this tissue. Typically, it isdesired to achieve a tissue temperature in the range of about 60° C. to100° C. to a depth of about 0.2 to 5 mm, usually about 1 to 2 mm. Thevoltage required for this thermal damage will partly depend on theelectrode configurations, the conductivity of the tissue and the areaimmediately surrounding the electrodes, the time period in which thevoltage is applied and the depth of tissue damage desired. With theelectrode configurations described in this application (e.g., FIGS.12-14), the voltage level for thermal heating will usually be in therange of about 20 to 300 volts rms, preferably about 60 to 200 voltsrms. The peak-to-peak voltages for thermal heating with a square waveform having a crest factor of about 2 are typically in the range ofabout 40 to 600 volts peak-to-peak, preferably about 120 to 400 voltspeak-to-peak. The higher the voltage is within this range, the less timerequired. If the voltage is too high, however, the surface tissue may bevaporized, debulked or ablated, which is undesirable.

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, peripheral or cranial nerves, e.g., opticnerve, facial nerves, vestibulocochlear nerves and the like. One of thesignificant drawbacks with the prior art microdebriders, conventionalelectrosurgical devices and lasers is that these devices do notdifferentiate between the target tissue and the surrounding nerves orbone. Therefore, the surgeon must be extremely careful during theseprocedures to avoid damage to the bone or nerves within and around thetarget site. In the present invention, the Coblation™ process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or epineurium,enclosing the bundles of nerve fibers, each bundle being surrounded byits own sheath of connective tissue (the perineurium) to protect thesenerve fibers. The outer protective tissue sheath or epineurium typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe turbinates, polyps, mucus tissue or the like, that are, for example,removed from the nose during sinus procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more electrode terminal(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the electrode terminal(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal tissue based on the measuredelectrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the electrode terminals will shut downor turn off when the electrical impedance reaches a threshold level.When this threshold level is set to the impedance of the fatty tissuesurrounding nerves, the electrode terminals will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother electrode terminals, which are in contact with or in closeproximity to tissue, will continue to conduct electric current to thereturn electrode. This selective ablation or removal of lower impedancetissue in combination with the Coblation™ mechanism of the presentinvention allows the surgeon to precisely remove tissue around nerves orbone. Applicant has found that the present invention is capable ofvolumetrically removing tissue closely adjacent to nerves withoutimpairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders, conventional electrosurgical devicesand lasers is that these devices do not differentiate between the targettissue and the surrounding nerves or bone. Therefore, the surgeon mustbe extremely careful during these procedures to avoid damage to the boneor nerves within and around the nasal cavity. In the present invention,the Coblation™ process for removing tissue results in extremely smalldepths of collateral tissue damage as discussed above. This allows thesurgeon to remove tissue close to a nerve without causing collateraldamage to the nerve fibers.

In addition to the above, applicant has discovered that the Coblation™mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the electrode terminal(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 1020 atoms/cm3 for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of electrode terminals;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break(typically on the order of about 8 eV). Accordingly, the presentinvention in its current configuration generally does not ablate orremove such fatty tissue. Of course, factors may be changed such thatthese double bonds can also be broken in a similar fashion as the singlebonds (e.g., increasing voltage or changing the electrode configurationto increase the current density at the electrode tips). A more completedescription of this phenomena can be found in co-pending U.S. patentapplication Ser. No. 09/032,375, filed Feb. 27, 1998 (Attorney DocketNo. CB-3), the complete disclosure of which is incorporated herein byreference.

The present invention also provides systems, apparatus and methods forselectively removing tumors, e.g., facial tumors, or other undesirablebody structures while minimizing the spread of viable cells from thetumor. Conventional techniques for removing such tumors generally resultin the production of smoke in the surgical setting, termed anelectrosurgical or laser plume, which can spread intact, viablebacterial or viral particles from the tumor or lesion to the surgicalteam or to other portions of the patient's body. This potential spreadof viable cells or particles has resulted in increased concerns over theproliferation of certain debilitating and fatal diseases, such ashepatitis, herpes, HIV and papillomavirus. In the present invention,high frequency voltage is applied between the electrode terminal(s) andone or more return electrode(s) to volumetrically remove at least aportion of the tissue cells in the tumor through the dissociation ordisintegration of organic molecules into non-viable atoms and molecules.Specifically, the present invention converts the solid tissue cells intonon-condensable gases that are no longer intact or viable, and thus, notcapable of spreading viable tumor particles to other portions of thepatient's brain or to the surgical staff. The high frequency voltage ispreferably selected to effect controlled removal of these tissue cellswhile minimizing substantial tissue necrosis to surrounding orunderlying tissue. A more complete description of this phenomena can befound in co-pending U.S. patent application Ser. No. 09/109,219, filedJun. 30, 1998 (Attorney Docket No. CB-1), the complete disclosure ofwhich is incorporated herein by reference.

In other procedures, e.g., soft palate or tongue/pharynx stiffening, itmay be desired to shrink or contract collagen connective tissue at thetarget site. In these procedures, the RF energy heats the tissuedirectly by virtue of the electrical current flow therethrough, and/orindirectly through the exposure of the tissue to fluid heated by RFenergy, to elevate the tissue temperature from normal body temperatures(e.g., 37° C.) to temperatures in the range of 45° C. to 90° C.,preferably in the range from about 60° C. to 70° C. Thermal shrinkage ofcollagen fibers occurs within a small temperature range which, formammalian collagen is in the range from 60° C. to 70° C. (Deak, G., etal., "The Thermal Shrinkage Process of Collagen Fibres as Revealed byPolarization Optical Analysis of Topooptical Staining Reactions," ActaMorphologica Acad. Sci. of Hungary, Vol. 15(2), pp 195-208, 1967).Collagen fibers typically undergo thermal shrinkage in the range of 60°C. to about 70° C. Previously reported research has attributed thermalshrinkage of collagen to the cleaving of the internal stabilizingcross-linkages within the collagen matrix (Deak, ibid). It has also beenreported that when the collagen temperature is increased above 70° C.,the collagen matrix begins to relax again and the shrinkage effect isreversed resulting in no net shrinkage (Allain, J. C., et al.,"Isometric Tensions Developed During the Hydrothermal Swelling of RatSkin," Connective Tissue Research, Vol. 7, pp 127-133, 1980).Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580 filed on Oct. 2, 1997, (Attorney DocketNo. 16238-001300).

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the tissue, (2) the location of nearby structures (e.g.,nerves) that should not be exposed to damaging temperatures, and/or (3)the location of the collagen tissue layer within which therapeuticshrinkage is to be effected. The depth of heating is usually in therange from 0 to 3.5 mm. In the case of collagen within the soft palateor uvula, the depth of heating is preferably in the range from about 0.5to about 3.5 mm.

The electrosurgical instrument will comprise a shaft or a handpiecehaving a proximal end and a distal end which supports one or moreelectrode terminal(s). The shaft or handpiece may assume a wide varietyof configurations, with the primary purpose being to mechanicallysupport the active electrode and permit the treating physician tomanipulate the electrode from a proximal end of the shaft. The shaft maybe rigid or flexible, with flexible shafts optionally being combinedwith a generally rigid external tube for mechanical support. Flexibleshafts may be combined with pull wires, shape memory actuators, andother known mechanisms for effecting selective deflection of the distalend of the shaft to facilitate positioning of the electrode array. Theshaft will usually include a plurality of wires or other conductiveelements running axially therethrough to permit connection of theelectrode array to a connector at the proximal end of the shaft.

For procedures within the mouth and throat, the shaft will have asuitable diameter and length to allow the surgeon to reach the target bydelivering the instrument shaft through the patient's mouth or anotheropening. Thus, the shaft will usually have a length in the range ofabout 5-25 cm, and a diameter in the range of about 0.5 to 5 mm. Forchanneling procedures or other procedures requiring the formation ofholes, channels or other spaces, the distal end portion of the shaftwill usually have a diameter less than 3 mm, preferably less than about1.0 mm. For procedures in the lower throat, such as laryngectomies,vocal cord papillomas or spasmodic dysphorias, the shaft will besuitably designed to access the larynx. For example, the shaft may beflexible, or have a distal bend to accommodate the bend in the patient'sthroat. In this regard, the shaft may be a rigid shaft having aspecifically designed bend to correspond with the geometry of the mouthand throat, or it may have a flexible distal end, or it may be part of acatheter. In any of these embodiments, the shaft may also be introducedthrough rigid or flexible endoscopes.

The electrosurgical instrument may also be a catheter that is deliveredpercutaneously and/or endoluminally into the patient by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode or electrode arrayintegral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter. Specific shaftdesigns will be described in detail in connection with the figureshereinafter.

The electrode terminal(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in the mouth and throat, however, makes a bipolardesign more preferable because this minimizes the current flow throughnon-target tissue and surrounding nerves. Accordingly, the returnelectrode is preferably either integrated with the instrument body, oranother instrument located in close proximity thereto. The proximal endof the instrument(s) will include the appropriate electrical connectionsfor coupling the return electrode(s) and the electrode terminal(s) to ahigh frequency power supply, such as an electrosurgical generator.

The return electrode is typically spaced proximally from the activeelectrode(s) a suitable distance to avoid electrical shorting betweenthe active and return electrodes in the presence of electricallyconductive fluid. In the embodiments described herein, the distal edgeof the exposed surface of the return electrode is spaced about 0.5 to 25mm from proximal edge of the exposed surface of the active electrode(s),preferably about 1.0 to 5.0 mm. Of course, this distance may vary withdifferent voltage ranges, conductive fluids, and depending on theproximity of tissue structures to active and return electrodes. Thereturn electrode will typically have an exposed length in the range ofabout 1 to 20 mm.

The current flow path between the electrode terminals and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conducting fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood or intracellular saline, may besufficient to establish a conductive path between the returnelectrode(s) and the electrode terminal(s), and to provide theconditions for establishing a vapor layer, as described above. However,conductive fluid that is introduced into the patient is generallypreferred over blood because blood will tend to coagulate at certaintemperatures. In addition, the patient's blood may not have sufficientelectrical conductivity to adequately form a plasma in someapplications. Advantageously, a liquid electrically conductive fluid(e.g., isotonic saline) may be used to concurrently "bathe" the targettissue surface to provide an additional means for removing any tissue,and to cool the region of the target tissue ablated in the previousmoment.

The power supply may include a fluid interlock for interrupting power tothe electrode terminal(s) when there is insufficient conductive fluidaround the electrode terminal(s). This ensures that the instrument willnot be activated when conductive fluid is not present, minimizing thetissue damage that may otherwise occur. A more complete description ofsuch a fluid interlock can be found in commonly assigned, co-pendingU.S. application Ser. No. 09/058,336, filed Apr. 10, 1998 (attorneyDocket No. CB-4), the complete disclosure of which is incorporatedherein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensible gaseousproducts of ablation. In addition, it may be desirable to aspirate smallpieces of tissue or other body structures that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention may include one ormore suction lumen(s) in the instrument, or on another instrument,coupled to a suitable vacuum source for aspirating fluids from thetarget site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation electrode terminal(s),or the same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, co-pending patent application entitled"Systems And Methods For Tissue Resection, Ablation And Aspiration",filed Jan. 21, 1998, the complete disclosure of which is incorporatedherein by reference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath or the like.This embodiment has the advantage of ensuring that the conductive fluid,tissue fragments or ablation products do not flow through the patient'svasculature or into other portions of the body. In addition, it may bedesirable to limit the amount of suction to limit the undesirable effectsuction may have on hemostasis of severed blood vessels.

The present invention may use a single active electrode terminal or anarray of electrode terminals spaced around the distal surface of acatheter or probe. In the latter embodiment, the electrode array usuallyincludes a plurality of independently current-limited and/orpower-controlled electrode terminals to apply electrical energyselectively to the target tissue while limiting the unwanted applicationof electrical energy to the surrounding tissue and environment resultingfrom power dissipation into surrounding electrically conductive fluids,such as blood, normal saline, and the like. The electrode terminals maybe independently current-limited by isolating the terminals from eachother and connecting each terminal to a separate power source that isisolated from the other electrode terminals. Alternatively, theelectrode terminals may be connected to each other at either theproximal or distal ends of the catheter to form a single wire thatcouples to a power source.

In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said instrument and is connected to apower source which is isolated from each of the other electrodeterminals in the array or to circuitry which limits or interruptscurrent flow to the electrode terminal when low resistivity material(e.g., blood, electrically conductive saline irrigant or electricallyconductive gel) causes a lower impedance path between the returnelectrode and the individual electrode terminal. The isolated powersources for each individual electrode terminal may be separate powersupply circuits having internal impedance characteristics which limitpower to the associated electrode terminal when a low impedance returnpath is encountered. By way of example, the isolated power source may bea user selectable constant current source. In this embodiment, lowerimpedance paths will automatically result in lower resistive heatinglevels since the heating is proportional to the square of the operatingcurrent times the impedance. Alternatively, a single power source may beconnected to each of the electrode terminals through independentlyactuatable switches, or by independent current limiting elements, suchas inductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the instrument, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the instrument. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form selected electrode terminals (e.g.,titanium or a resistive coating on the surface of metal, such asplatinum).

The tip region of the instrument may comprise many independent electrodeterminals designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual electrode terminal andthe return electrode to a power source having independently controlledor current limited channels. The return electrode(s) may comprise asingle tubular member of conductive material proximal to the electrodearray at the tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the electrode terminals withconduction of high frequency current from each individual electrodeterminal to the return electrode. The current flow from each individualelectrode terminal to the return electrode(s) is controlled by eitheractive or passive means, or a combination thereof, to deliver electricalenergy to the surrounding conductive fluid while minimizing energydelivery to surrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may be moreprecisely controlled, for example, by the use of a multiplicity of smallelectrode terminals whose effective diameters or principal dimensionsrange from about 10 mm to 0.01 mm, preferably from about 2 mm to 0.05mm, and more preferably from about 1 mm to 0.1 mm. In this embodiment,electrode areas for both circular and non-circular terminals will have acontact area (per electrode terminal) below 50 mm2 for electrode arraysand as large as 75 mm2 for single electrode embodiments. In multipleelectrode arrays, the contact area of each electrode terminal istypically in the range from 0.0001 mm2 to 1 mm2, and more preferablyfrom 0.001 mm2 to 0.5 mm2. The circumscribed area of the electrode arrayor electrode terminal is in the range from 0.25 mm2 to 75 mm2,preferably from 0.5 mm2 to 40 mm2. In multiple electrode embodiments,the array will usually include at least two isolated electrodeterminals, often at least five electrode terminals, often greater than10 electrode terminals and even 50 or more electrode terminals, disposedover the distal contact surfaces on the shaft. The use of small diameterelectrode terminals increases the electric field intensity and reducesthe extent or depth of tissue heating as a consequence of the divergenceof current flux lines which emanate from the exposed surface of eachelectrode terminal.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Thegeometries can be planar, concave, convex, hemispherical, conical,linear "in-line" array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or electrode terminal(s)will be formed at the distal tip of the electrosurgical instrumentshaft, frequently being planar, disk-shaped, or hemispherical surfacesfor use in reshaping procedures or being linear arrays for use incutting. Alternatively or additionally, the active electrode(s) may beformed on lateral surfaces of the electrosurgical instrument shaft(e.g., in the manner of a spatula), facilitating access to certain bodystructures in endoscopic procedures.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the electrode terminal(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between theelectrode terminal(s) and the tissue at the treatment site throughoutthe procedure, which reduces the thermal damage that might otherwiseoccur if the vapor layer were extinguished due to a lack of conductivefluid. Provision of the electrically conductive fluid around the targetsite also helps to maintain the tissue temperature at desired levels.

In other embodiments, the active electrodes are spaced from the tissue asufficient distance to minimize or avoid contact between the tissue andthe vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe electrode terminal(s). The electrical conductivity of the fluid (inunits of milliSiemans per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

The voltage difference applied between the return electrode(s) and theelectrode terminal(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, often lessthan 350 kHz, and often between about 100 kHz and 200 kHz. In someapplications, applicant has found that a frequency of about 100 kHz isuseful because the tissue impedance is much greater at this frequency.In other applications, such as procedures in or around the heart or headand neck, higher frequencies may be desirable (e.g., 400-600 kHz) tominimize low frequency current flow into the heart or the nerves of thehead and neck. The RMS (root mean square) voltage applied will usuallybe in the range from about 5 volts to 1000 volts, preferably being inthe range from about 10 volts to 500 volts, often between about 150 to400 volts depending on the electrode terminal size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation, cutting orablation). Typically, the peak-to-peak voltage for ablation or cuttingwith a square wave form will be in the range of 10 to 2000 volts andpreferably in the range of 100 to 1800 volts and more preferably in therange of about 300 to 1500 volts, often in the range of about 300 to 800volts peak to peak (again, depending on the electrode size, number ofelectrons, the operating frequency and the operation mode). Lowerpeak-to-peak voltages will be used for tissue coagulation, thermalheating of tissue, or collagen contraction and will typically be in therange from 50 to 1500, preferably 100 to 1000 and more preferably 120 to400 volts peak-to-peak (again, these values are computed using a squarewave form). Higher peak-to-peak voltages, e.g., greater than about 800volts peak-to-peak, may be desirable for ablation of harder material,such as bone, depending on other factors, such as the electrodegeometries and the composition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular neurosurgery procedure, cardiac surgery, arthroscopicsurgery, dermatological procedure, ophthalmic procedures, open surgeryor other endoscopic surgery procedure. For cardiac procedures andpotentially for neurosurgery, the power source may have an additionalfilter, for filtering leakage voltages at frequencies below 100 kHz,particularly voltages around 60 kHz. Alternatively, a power sourcehaving a higher operating frequency, e.g., 300 to 600 kHz may be used incertain procedures in which stray low frequency currents may beproblematic. A description of one suitable power source can be found inco-pending patent application Ser. No. 09/058,571 and 09/058,336, filedApr. 10, 1998 (Attorney Docket Nos. CB-2 and CB-4), the completedisclosure of both applications are incorporated herein by reference forall purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent electrode terminal, where the inductance of theinductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in U.S. Pat.No. 5,697,909, the complete disclosure of which is incorporated hereinby reference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual electrode terminal in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said electrode terminal into the low resistance medium(e.g., saline irrigant or blood).

It should be clearly understood that the invention is not limited toelectrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through thecatheter shaft to a power source of high frequency current.Alternatively, the instrument may incorporate a single electrode thatextends directly through the catheter shaft or is connected to a singlelead that extends to the power source. The active electrode(s) may haveball shapes (e.g., for tissue vaporization and desiccation), twizzleshapes (for vaporization and needle-like cutting), spring shapes (forrapid tissue debulking and desiccation), twisted metal shapes, annularor solid tube shapes or the like. Alternatively, the electrode(s) maycomprise a plurality of filaments, rigid or flexible brush electrode(s)(for debulking a tumor, such as a fibroid, bladder tumor or a prostateadenoma), side-effect brush electrode(s) on a lateral surface of theshaft, coiled electrode(s) or the like.

In one embodiment, an electrosurgical catheter or probe comprises asingle active electrode terminal that extends from an insulating member,e.g., ceramic, at the distal end of the shaft. The insulating member ispreferably a tubular structure that separates the active electrodeterminal from a tubular or annular return electrode positioned proximalto the insulating member and the active electrode. In anotherembodiment, the catheter or probe includes a single active electrodethat can be rotated relative to the rest of the catheter body, or theentire catheter may be rotated related to the lead. The single activeelectrode can be positioned adjacent the abnormal tissue and energizedand rotated as appropriate to remove this tissue.

The current flow path between the electrode terminal(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting media (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the electrode terminal to the returnelectrode.

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the head and neck will now be described indetail. Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site and a fluid source 21 for supplyingelectrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly insinus procedures or procedures in the ear or the back of the mouth. Theendoscope may be integral with probe 10, or it may be part of a separateinstrument. The system 11 may also include a vacuum source (not shown)for coupling to a suction lumen or tube 205 (see FIG. 2) in the probe 10for aspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of electrode terminals 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the electrode terminals 58 to power supply 28. The electrodeterminals 58 are electrically isolated from each other and each of theterminals 58 is connected to an active or passive control network withinpower supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conducting fluid 50 tothe target site. Fluid supply tube 15 may be connected to a suitablepump (not shown), if desired.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to electrode terminals 58. Inan exemplary embodiment, first foot pedal 37 is used to place the powersupply into the "ablation" mode and second foot pedal 38 places powersupply 28 into the "sub-ablation" mode (e.g., coagulation or contractionof tissue). The third foot pedal 39 allows the user to adjust thevoltage level within the "ablation" mode. In the ablation mode, asufficient voltage is applied to the electrode terminals to establishthe requisite conditions for molecular dissociation of the tissue (i.e.,vaporizing a portion of the electrically conductive fluid, ionizingcharged particles within the vapor layer and accelerating these chargedparticles against the tissue). As discussed above, the requisite voltagelevel for ablation will vary depending on the number, size, shape andspacing of the electrodes, the distance in which the electrodes extendfrom the support member, etc. Once the surgeon places the power supplyin the "ablation" mode, voltage level adjustment 30 or third foot pedal39 may be used to adjust the voltage level to adjust the degree oraggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the subablation mode, the power supply 28 applies a low enoughvoltage to the electrode terminals to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and sub-ablation modes by alternatively stepping onfoot pedals 37, 38, respectively. In some embodiments, this allows thesurgeon to quickly move between coagulation/thermal heating and ablationin situ, without having to remove his/her concentration from thesurgical field or without having to request an assistant to switch thepower supply. By way of example, as the surgeon is sculpting soft tissuein the ablation mode, the probe typically will simultaneously sealand/or coagulation small severed vessels within the tissue. However,larger vessels, or vessels with high fluid pressures (e.g., arterialvessels) may not be sealed in the ablation mode. Accordingly, thesurgeon can simply step on foot pedal 38, automatically lowering thevoltage level below the threshold level for ablation, and applysufficient pressure onto the severed vessel for a sufficient period oftime to seal and/or coagulate the vessel. After this is completed, thesurgeon may quickly move back into the ablation mode by stepping on footpedal 37. A specific design of a suitable power supply for use with thepresent invention can be found in U.S. Provisional Patent ApplicationNo. 60/062,997, filed Oct. 23, 1997 (attorney docket no. 16238-007400),previously incorporated herein by reference.

Referring now to FIGS. 22 and 23, a representative high frequency powersupply for use according to the principles of the present invention willnow be described. The high frequency power supply of the presentinvention is configured to apply a high frequency voltage of about 10 to500 volts RMS between one or more electrode terminals (and/orcoagulation electrode) and one or more return electrodes. In theexemplary embodiment, the power supply applies about 70-350 volts RMS inthe ablation mode and about 20 to 90 volts in a subablation mode,preferably 45 to 70 volts in the subablation mode (these values will, ofcourse, vary depending on the probe configuration attached to the powersupply and the desired mode of operation).

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the probe tip. The power source allows the userto select the voltage level according to the specific requirements of aparticular procedure, e.g., arthroscopic surgery, dermatologicalprocedure, ophthalmic procedures, open surgery or other endoscopicsurgery procedure.

As shown in FIG. 22, the power supply generally comprises a radiofrequency (RF) power oscillator 100 having output connections forcoupling via a power output signal 102 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300kHz to 600kHz. In particular, forcardiac applications, the RF oscillator will preferably operate in therange of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 102 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to theelectrode terminals and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

Power is supplied to the oscillator 100 by a switching power supply 104coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 140 allows thegenerator to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 104 operates at about100 kHz.

A controller 106 coupled to the operator controls 105 (i.e., foot pedalsand voltage selector) and display 116, is connected to a control inputof the switching power supply 104 for adjusting the generator outputpower by supply voltage variation. The controller 106 may be amicroprocessor or an integrated circuit. The power supply may alsoinclude one or more current sensors 112 for detecting the outputcurrent. The power supply is preferably housed within a metal casingwhich provides a durable enclosure for the electrical componentstherein. In addition, the metal casing reduces the electromagnetic noisegenerated within the power supply because the grounded metal casingfunctions as a "Faraday shield", thereby shielding the environment frominternal sources of electromagnetic noise.

The power supply generally comprises a main or mother board containinggeneric electrical components required for many different surgicalprocedures (e.g., arthroscopy, urology, general surgery, dermatology,neurosurgery, etc.), and a daughter board containing applicationspecific current-limiting circuitry (e.g., inductors, resistors,capacitors and the like). The daughter board is coupled to the motherboard by a detachable multi-pin connector to allow convenient conversionof the power supply to, e.g., applications requiring a different currentlimiting circuit design. For arthroscopy, for example, the daughterboard preferably comprises a plurality of inductors of about 200 to 400microhenries, usually about 300 microhenries, for each of the channelssupplying current to the electrode terminals 02 (see FIG. 2).

Alternatively, in one embodiment, current limiting inductors are placedin series with each independent electrode terminal, where the inductanceof the inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors willhave a large positive temperature coefficient of resistance so that, asthe current level begins to rise for any individual electrode terminalin contact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidelectrode terminal into the low resistance medium (e.g., saline irrigantor conductive gel). Power output signal may also be coupled to aplurality of current limiting elements 96, which are preferably locatedon the daughter board since the current limiting elements may varydepending on the application.

FIGS. 2-4 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.2, probe 90 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises an electrically conducting material,usually metal, which is selected from the group comprising tungsten,stainless steel alloys, platinum or its alloys, titanium or its alloys,molybdenum or its alloys, and nickel or its alloys. In this embodiment,shaft 100 includes an electrically insulating jacket 108, which istypically formed as one or more electrically insulating sheaths orcoatings, such as polytetrafluoroethylene, polyimide, and the like. Theprovision of the electrically insulating jacket over the shaft preventsdirect electrical contact between these metal elements and any adjacentbody structure or the surgeon. Such direct electrical contact between abody structure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 4), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 to 20 mm),and provides support for a plurality of electrically isolated electrodeterminals 104 (see FIG. 3). As shown in FIG. 2, a fluid tube 233 extendsthrough an opening in handle 204, and includes a connector 235 forconnection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Depending on the configuration ofthe distal surface of shaft 100, fluid tube 233 may extend through asingle lumen (not shown) in shaft 100, or it may be coupled to aplurality of lumens (also not shown) that extend through shaft 100 to aplurality of openings at its distal end. In the representativeembodiment, fluid tube 239 is a peek tubing that extends along theexterior of shaft 100 to a point just distal of return electrode 112(see FIG. 3). In this embodiment, the fluid is directed through anopening 237 past return electrode 112 to the electrode terminals 104.Probe 20 may also include a valve 17 (FIG. 1) or equivalent structurefor controlling the flow rate of the electrically conducting fluid tothe target site.

As shown in FIG. 2, the distal portion of shaft 100 is preferably bentto improve access to the operative site of the tissue being treated.Electrode support member 102 has a substantially planar tissue treatmentsurface 212 (FIG. 3) that is usually at an angle of about 10 to 90degrees relative to the longitudinal axis of shaft 100, preferably about30 to 60 degrees and more preferably about 45 degrees. In alternativeembodiments, the distal portion of shaft 100 comprises a flexiblematerial which can be deflected relative to the longitudinal axis of theshaft. Such deflection may be selectively induced by mechanical tensionof a pull wire, for example, or by a shape memory wire that expands orcontracts by externally applied temperature changes. A more completedescription of this embodiment can be found in U.S. Pat. No. 5,697,909,the complete disclosure of which has previously been incorporated hereinby reference.

In the embodiment shown in FIGS. 2-4, probe 90 includes a returnelectrode 112 for completing the current path between electrodeterminals 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an exposed portion ofshaft 100 shaped as an annular conductive band near the distal end ofshaft 100 slightly proximal to tissue treatment surface 212 of electrodesupport member 102, typically about 0.5 to 10 mm and more preferablyabout 1 to 10 mm. Return electrode 112 or shaft 100 is coupled to aconnector 258 that extends to the proximal end of probe 10, where it issuitably connected to power supply 10 (FIG. 1).

As shown in FIG. 2, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that electrodeterminals 104 are electrically connected to return electrode 112,electrically conducting fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through fluid tube 233 to opening 237, asdescribed above. Alternatively, the fluid may be delivered by a fluiddelivery element (not shown) that is separate from probe 20. Inarthroscopic surgery, for example, the body cavity will be flooded withisotonic saline and the probe 90 will be introduced into this floodedcavity. Electrically conducting fluid will be continually resupplied tomaintain the conduction path between return electrode 112 and electrodeterminals 104. In other embodiments, the distal portion of probe 20 maybe dipped into a source of electrically conductive fluid, such as a gelor isotonic saline, prior to positioning at the target site. Applicanthas found that surface tension of the fluid and/or the viscous nature ofa gel allows the conductive fluid to remain around the active and returnelectrodes for long enough to complete its function according to thepresent invention, as described below. Alternatively, the conductivefluid, such as a gel, may be applied directly to the target site.

In alternative embodiments, the fluid path may be formed in probe 90 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIG. 5).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conducting fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in U.S. Pat. No.5,697,281, the complete disclosure of which has previously beenincorporated herein by reference.

Referring to FIG. 3, the electrically isolated electrode terminals 104are spaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual electrodeterminals 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range of1 mm to 20. The individual electrode terminals 104 preferably extendoutward from tissue treatment surface 212 by a distance of about 0.1 to4 mm, usually about 0.2 to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around electrode terminals 104 tofacilitate the ablation of tissue as described in detail above.

In the embodiment of FIGS. 2-4, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of electrode terminals (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 3). Alternatively, the probe may include asingle, annular, or partially annular, electrode terminal at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction lumen (not shown) within shaft 100 and a suctiontube 211 (FIG. 2) for aspirating tissue, fluids and/or gases from thetarget site. In this embodiment, the electrically conductive fluidgenerally flows radially inward past electrode terminals 104 and thenback through the opening 209. Aspirating the electrically conductivefluid during surgery allows the surgeon to see the target site, and itprevents the fluid from flowing into the patient's body, e.g., throughthe sinus passages, down the patient's throat or into the ear canal.

Of course, it will be recognized that the distal tip of probe may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (see FIG. 6). In this embodiment, the electrodeterminals 104 extend from the center of tissue treatment surface 212radially inward from openings 209. The openings are suitably coupled tofluid tube 233 for delivering electrically conductive fluid to thetarget site, and suction tube 211 for aspirating the fluid after it hascompleted the conductive path between the return electrode 112 and theelectrode terminals 104.

FIG. 4 illustrates the electrical connections 250 within handle 204 forcoupling electrode terminals 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple terminals 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a plug 260.

According to the present invention, the probe 20 further includes anidentification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe 20 includes a voltage reduction element or a voltage reductioncircuit for reducing the voltage applied between the electrode terminals104 and the return electrode 112. The voltage reduction element servesto reduce the voltage applied by the power supply so that the voltagebetween the electrode terminals and the return electrode is low enoughto avoid excessive power dissipation into the electrically conductingmedium and/or ablation of the soft tissue at the target site. Thevoltage reduction element primarily allows the electrosurgical probe 90to be compatible with other ArthroCare generators that are adapted toapply higher voltages for ablation or vaporization of tissue. Forthermal heating or coagulation of tissue, for example, the voltagereduction element will serve to reduce a voltage of about 100 to 170volts rms (which is a setting of 1 or 2 on the ArthroCare Model 970 and980 (i.e., 2000) Generators) to about 45 to 60 volts rms, which is asuitable voltage for coagulation of tissue without ablation (e.g.,molecular dissociation) of the tissue.

Of course, for some procedures, such as endoscopic sinus surgery, theprobe will typically not require a voltage reduction element.Alternatively, the probe may include a voltage increasing element orcircuit, if desired. Alternatively or additionally, the cable 22 thatcouples the power supply 10 to the probe 90 may be used as a voltagereduction element. The cable has an inherent capacitance that can beused to reduce the power supply voltage if the cable is placed into theelectrical circuit between the power supply, the electrode terminals andthe return electrode. In this embodiment, the cable 22 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor. Further, it should be noted that thepresent invention can be used with a power supply that is adapted toapply a voltage within the selected range for treatment of tissue. Inthis embodiment, a voltage reduction element or circuitry may not bedesired.

FIGS. 7A-7C schematically illustrate the distal portion of threedifferent embodiments of probe 90 according to the present invention. Asshown in 7A, electrode terminals 104 are anchored in a support matrix102 of suitable insulating material (e.g., ceramic or glass material,such as alumina, zirconia and the like) which could be formed at thetime of manufacture in a flat, hemispherical or other shape according tothe requirements of a particular procedure. The preferred support matrixmaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support matrix 102 is adhesively joined to a tubular support member78 that extends most or all of the distance between matrix 102 and theproximal end of probe 90. Tubular member 78 preferably comprises anelectrically insulating material, such as an epoxy or silicone-basedmaterial.

In a preferred construction technique, electrode terminals 104 extendthrough pre-formed openings in the support matrix 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport matrix 102, typically by an inorganic sealing material 80.Sealing material 80 is selected to provide effective electricalinsulation, and good adhesion to both the alumina matrix 102 and theplatinum or titanium electrode terminals. Sealing material 80additionally should have a compatible thermal expansion coefficient anda melting point well below that of platinum or titanium and alumina orzirconia, typically being a glass or glass ceramic.

In the embodiment shown in FIG. 7A, return electrode 112 comprises anannular member positioned around the exterior of shaft 100 of probe 90.Return electrode 90 may fully or partially circumscribe tubular supportmember 78 to form an annular gap 54 therebetween for flow ofelectrically conducting liquid 50 therethrough, as discussed below. Gap54 preferably has a width in the range of 0.25 mm to 4 mm.Alternatively, probe may include a plurality of longitudinal ribsbetween support member 78 and return electrode 112 to form a pluralityof fluid lumens extending along the perimeter of shaft 100. In thisembodiment, the plurality of lumens will extend to a plurality ofopenings.

Return electrode 112 is disposed within an electrically insulativejacket 18, which is typically formed as one or more electricallyinsulative sheaths or coatings, such as polytetrafluoroethylene,polyamide, and the like. The provision of the electrically insulativejacket 18 over return electrode 112 prevents direct electrical contactbetween return electrode 56 and any adjacent body structure. Such directelectrical contact between a body structure (e.g., tendon) and anexposed electrode member 112 could result in unwanted heating andnecrosis of the structure at the point of contact causing necrosis.

As shown in FIG. 7A, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that terminals104 are electrically connected to return electrode 112, electricallyconducting liquid 50 (e.g., isotonic saline) is caused to flow alongfluid path(s) 83. Fluid path 83 is formed by annular gap 54 betweenouter return electrode 112 and tubular support member. The electricallyconducting liquid 50 flowing through fluid path 83 provides a pathwayfor electrical current flow between electrode terminals 104 and returnelectrode 112, as illustrated by the current flux lines 60 in FIG. 6A.When a voltage difference is applied between electrode terminals 104 andreturn electrode 112, high electric field intensities will be generatedat the distal tips of terminals 104 with current flow from terminals 104through the target tissue to the return electrode, the high electricfield intensities causing ablation of tissue 52 in zone 88.

FIG. 7B illustrates another alternative embodiment of electrosurgicalprobe 90 which has a return electrode 112 positioned within tubularmember 78. Return electrode 112 is preferably a tubular member definingan inner lumen 57 for allowing electrically conducting liquid 50 (e.g.,isotonic saline) to flow therethrough in electrical contact with returnelectrode 112. In this embodiment, a voltage difference is appliedbetween electrode terminals 104 and return electrode 112 resulting inelectrical current flow through the electrically conducting liquid 50 asshown by current flux lines 60 (FIG. 3). As a result of the appliedvoltage difference and concomitant high electric field intensities atthe tips of electrode terminals 104, tissue 52 becomes ablated ortransected in zone 88.

FIG. 7C illustrates another embodiment of probe 90 that is a combinationof the embodiments in FIGS. 7A and 7B. As shown, this probe includesboth an inner lumen 57 and an outer gap or plurality of outer lumens 54for flow of electrically conductive fluid. In this embodiment, thereturn electrode 112 may be positioned within tubular member 78 as inFIG. 7B, outside of tubular member 78 as in FIG. 7A, or in bothlocations.

FIG. 9 illustrates another embodiment of probe 90 where the distalportion of shaft 100 is bent so that electrode terminals extendtransversely to the shaft. Preferably, the distal portion of shaft 100is perpendicular to the rest of the shaft so that tissue treatmentsurface 212 is generally parallel to the shaft axis. In this embodiment,return electrode 112 is mounted to the outer surface of shaft 100 and iscovered with an electrically insulating jacket 18. The electricallyconducting fluid 50 flows along flow path 83 through return electrode112 and exits the distal end of electrode 112 at a point proximal oftissue treatment surface 212. The fluid is directed exterior of shaft tosurface 212 to create a return current path from electrode terminals104, through the fluid 50, to return electrode 12, as shown by currentflux lines 60.

FIG. 10 illustrates another embodiment of the invention whereelectrosurgical system 11 further includes a liquid supply instrument 64for supplying electrically conducting fluid 50 between electrodeterminals 104 and return electrode 112. Liquid supply instrument 64comprises an inner tubular member or return electrode 112 surrounded byan electrically insulating jacket 18. Return electrode 112 defines aninner passage 83 for flow of fluid 50. As shown in FIG. 8, the distalportion of instrument 64 is preferably bent so that liquid 50 isdischarged at an angle with respect to instrument 64. This allows thesurgical team to position liquid supply instrument 64 adjacent tissuetreatment surface 212 with the proximal portion of supply instrument 64oriented at a similar angle to probe 90.

The present invention is not limited to an electrode array disposed on arelatively planar surface at the distal tip of probe 90, as describedabove. Referring to FIGS. 8A and 8B, an alternative probe 90 includes apair of electrodes 105a, 105b mounted to the distal end of shaft 100.Electrodes 105a, 105b are electrically connected to power supply asdescribed above and preferably have tips 107a, 107b with a screwdrivershape. The screwdriver shape provides a greater amount of "edges" toelectrodes 105a, 105b, to increase the electric field intensity andcurrent density at the edges and thereby improve the cutting ability aswell as the ability to limit bleeding from the incised tissue (i.e.,hemostasis).

FIGS. 11A and 11B illustrate the present invention in the ablation mode.As shown, the high frequency voltage difference applied between theactive electrodes 104 (single active electrode 104 in FIG. 11B) and thereturn electrode 112 is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue 302 and electrodeterminal(s) 104 into an ionized vapor layer 312 or plasma. As a resultof the applied voltage difference between electrode terminal(s) 104 andthe target tissue 302 (i.e., the voltage gradient across the plasmalayer 312), charged particles 315 in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles 315 gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases 314, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles 315 withinthe tissue confines the molecular dissociation process to the surfacelayer to minimize damage and necrosis to the underlying tissue 320.

In some embodiments, the gases 314 will be aspirated through opening 209and suction tube 211 (see FIGS. 2 and 3) to a vacuum source. Inaddition, excess electrically conductive fluid, and other fluids (e.g.,blood) will be aspirated from the target site 300 to facilitate thesurgeon's view. During ablation of the tissue, the residual heatgenerated by the current flux lines (typically less than 150° C.), willusually be sufficient to coagulate any severed blood vessels at thesite. If not, the surgeon may switch the power supply 28 into thecoagulation mode by lowering the voltage to a level below the thresholdfor fluid vaporization, as discussed above. This simultaneous hemostasisresults in less bleeding and facilitates the surgeon's ability toperform the procedure. Once the blockage has been removed, aeration anddrainage are reestablished to allow the sinuses to heal and return totheir normal function.

FIGS. 12A-12C and 13 illustrate embodiments of an electrosurgical probe350 specifically designed for the treatment of obstructive sleepdisorders, such as sleep apnea or snoring. Referring to FIG. 12A, probe350 comprises an electrically conductive shaft 352, a handle 354 coupledto the proximal end of shaft 352 and an electrically insulating supportmember 356 at the distal end of shaft 352. Probe 350 further includes ashrink wrapped insulating sleeve 358 over shaft 352, and exposed portionof shaft 352 that functions as the return electrode 360. In therepresentative embodiment, probe 350 comprises a plurality of activeelectrodes 362 extending from the distal end of support member 356. Asshown, return electrode 360 is spaced a further distance from activeelectrodes 362 than in the embodiments described above. In thisembodiment, the return electrode 360 is spaced a distance of about 2.0to 50 mm, preferably about 5 to 25 mm. In addition, return electrode 360has a larger exposed surface area than in previous embodiments, having alength in the range of about 2.0 to 40 mm, preferably about 5 to 20 mm.Accordingly, electric current passing from active electrodes 362 toreturn electrode 360 will follow a current flow path 370 that is furtheraway from shaft 352 than in the previous embodiments. In someapplications, this current flow path 370 results in a deeper currentpenetration into the surrounding tissue with the same voltage level, andthus increased thermal heating of the tissue. As discussed above, thisincreased thermal heating may have advantages in some applications oftreating obstructive sleep disorders. Typically, it is desired toachieve a tissue temperature in the range of about 60° C. to 100° C. toa depth of about 0.2 to 5 mm, usually about 1 to 2 mm. The voltagerequired for this thermal damage will partly depend on the electrodeconfigurations, the conductivity of the tissue and the area immediatelysurrounding the electrodes, the time period in which the voltage isapplied and the depth of tissue damage desired. With the electrodeconfigurations described in FIGS. 12-14, the voltage level for thermalheating will usually be in the range of about 20 to 300 volts rms,preferably about 60 to 200 volts rms. The peak-to-peak voltages forthermal heating with a square wave form having a crest factor of about 2are typically in the range of about 40 to 600 volts peak-to-peak,preferably about 120 to 400 volts peak-to-peak. The higher the voltageis within this range, the less time required. If the voltage is toohigh, however, the surface tissue may be vaporized, debulked or ablated,which is undesirable.

In alternative embodiments, the electrosurgical system used inconjunction with probe 350 may include a dispersive return electrode 450(see FIG. 14) for switching between bipolar and monopolar modes. In thisembodiment, the system will switch between an ablation mode, where thedispersive pad 450 is deactivated and voltage is applied between activeand return electrodes 362, 360, and a subablation or thermal heatingmode, where the active electrode(s) 362 and deactivated and voltage isapplied between the dispersive pad 450 and the return electrode 360. Inthe subablation mode, a lower voltage is typically applied and thereturn electrode 360 functions as the active electrode to providethermal heating and/or coagulation of tissue surrounding returnelectrode 360.

FIG. 12B illustrates yet another embodiment of the present invention. Asshown, electrosurgical probe 350 comprises an electrode assembly 372having one or more active electrode(s) 362 and a proximally spacedreturn electrode 360 as in previous embodiments. Return electrode 360 istypically spaced about 0.5 to 25 mm, preferably 1.0 to 5.0 mm from theactive electrode(s) 362, and has an exposed length of about 1 to 20 mm.In addition, electrode assembly 372 includes two additional electrodes374, 376 spaced axially on either side of return electrode 360.Electrodes 374, 376 are typically spaced about 0.5 to 25 mm, preferablyabout 1 to 5 mm from return electrode 360. In the representativeembodiment, the additional electrodes 374, 376 are exposed portions ofshaft 352, and the return electrode 360 is electrically insulated fromshaft 352 such that a voltage difference may be applied betweenelectrodes 374, 376 and electrode 360. In this embodiment, probe 350 maybe used in at least two different modes, an ablation mode and asubablation or thermal heating mode. In the ablation mode, voltage isapplied between active electrode(s) 362 and return electrode 360 in thepresence of electrically conductive fluid, as described above. In theablation mode, electrodes 374, 376 are deactivated. In the thermalheating or coagulation mode, active electrode(s) 362 are deactivated anda voltage difference is applied between electrodes 374, 376 andelectrode 360 such that a high frequency current 370 flows therebetween,as shown in FIG. 12B. In the thermal heating mode, a lower voltage istypically applied below the threshold for plasma formation and ablation,but sufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue so that the current 370 provides thermal heating and/orcoagulation of tissue surrounding electrodes 360, 372, 374.

FIG. 12C illustrates another embodiment of probe 350 incorporating anelectrode assembly 372 having one or more active electrode(s) 362 and aproximally spaced return electrode 360 as in previous embodiments.Return electrode 360 is typically spaced about 0.5 to 25 mm, preferably1.0 to 5.0 mm from the active electrode(s) 362, and has an exposedlength of about 1 to 20 mm. In addition, electrode assembly 372 includesa second active electrode 380 separated from return electrode 360 by anelectrically insulating spacer 382. In this embodiment, handle 354includes a switch 384 for toggling probe 350 between at least twodifferent modes, an ablation mode and a subablation or thermal heatingmode. In the ablation mode, voltage is applied between activeelectrode(s) 362 and return electrode 360 in the presence ofelectrically conductive fluid, as described above. In the ablation mode,electrode 380 deactivated. In the thermal heating or coagulation mode,active electrode(s) 362 may be deactivated and a voltage difference isapplied between electrode 380 and electrode 360 such that a highfrequency current 370 flows therebetween. Alternatively, activeelectrode(s) 362 may not be deactivated as the higher resistance of thesmaller electrodes may automatically send the electric current toelectrode 380 without having to physically decouple electrode(s) 362from the circuit. In the thermal heating mode, a lower voltage istypically applied below the threshold for plasma formation and ablation,but sufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue so that the current 370 provides thermal heating and/orcoagulation of tissue surrounding electrodes 360, 380.

Of course, it will be recognized that a variety of other embodiments maybe used to accomplish similar functions as the embodiments describedabove. For example, electrosurgical probe 350 may include a plurality ofhelical bands formed around shaft 352, with one or more of the helicalbands having an electrode coupled to the portion of the band such thatone or more electrodes are formed on shaft 352 spaced axially from eachother.

FIG. 13 illustrates yet another embodiment of the present invention forforming small channels or holes in tissue, as described in more detailbelow. In this embodiment, an exemplary electrosurgical probe 510comprises a handle 519, which preferably comprises a disposable distalportion 513 removably coupled to a proximal reusable portion 512, and anelongate shaft 517 extending from distal portion 513 of handle 519.Shaft 517 is also disposable, and preferably removably coupled to distalportion 513 of the handle. The proximal and distal portions of handle512 typically comprise a plastic material that is easily molded into asuitable shape for handling by the surgeon. Handle 519 defines an innercavity (not shown) that houses the electrical connections 574, andprovides a suitable interface for connection to an electrical connectingcable (not shown). In the exemplary embodiment, the proximal portion ofhandle 519 is constructed so that it can be re-used by sterilizinghandle 519 between surgical procedures. However, it should be understoodthat both the proximal and distal portions of handle 519 may bereusable, or both of these handle portions may be disposable, ifdesired.

Shaft 517 is preferably sized to provide access to the patient's mouthand throat, typically through the patient's mouth. Accordingly, shaft517 preferably has a length in the range of about 4 to 25 cm and adiameter less than 1 cm. For treating obstructive sleep disorders, theshaft 517 will also preferably be sized for forming small holes orchannels in the tongue, palate, tonsils and/or uvula and, therefore,will have a diameter less than 3 mm, preferably less than about 1 mm.Alternatively, shaft 517 may have a distal portion that is smaller thanthe rest of shaft for forming such holes. As shown in FIG. 13, shaft 517includes an electrically insulating electrode support member 570extending from the distal end of shaft 517 (usually about 0.5 to 20 mm)to provide support for a plurality of electrically isolated electrodeterminals 558. Alternatively, electrode support member 570 may berecessed from the distal end of shaft 517 to help confine theelectrically conductive fluid around the electrode terminals 558 duringthe surgical procedure, as discussed above.

In the embodiment shown in FIG. 13, probe 510 includes an annular returnelectrode 572 for completing the current path between electrodeterminals 558 and a high frequency power supply 28. Return electrode 572is spaced proximally from electrode terminal(s) 558 a sufficientdistance to avoid arcing therebetween. In addition, return electrode 572is positioned such that, when electrode terminal(s) 558 are broughtadjacent a tissue structure, return electrode 572 is spaced away fromthe tissue structure so that the tissue structure cannot, at least byitself, complete the current flow path between electrode terminal(s) 558and return electrode 572.

To complete the current path between electrode terminals 558 and returnelectrode 572, electrically conducting fluid (e.g., isotonic saline orelectrically conducting gel) is located between the active and returnelectrodes during a surgical procedure. In the representativeembodiment, probe 510 includes a fluid tube 511 for deliveringelectrically conductive fluid to the target site. Fluid tube 511 issized to extend through a groove 514 in handle 511 and through an innercavity (not shown) in shaft 517 to a distal opening (not shown) locatedadjacent electrode support member 570. Tube 510 preferably extends allthe way through the inner cavity to the distal opening to eliminate anypossible fluid ingress into the cavity. As shown in FIG. 13, fluid tube511 includes a proximal connector 512 for coupling to an electricallyconductive fluid source (not shown). Probe 510 will also include a valveor equivalent structure for controlling the flow rate of theelectrically conducting fluid to the target site. In the representativeembodiment, handle 19 comprises a main body 518, 520 and a rotatablesleeve 516 for controlling fluid flow through tube 511. Rotation ofsleeve 516 crimps tube 511 to limit or complete shut off flowtherethrough. Of course, this fluid control may be provided by a varietyof other input and valve devices, such as switches, buttons, etc.

FIG. 14 illustrates yet another embodiment of an electrosurgical system440 incorporating a dispersive return pad 450 attached to theelectrosurgical probe 400. In this embodiment, the invention functionsin the bipolar mode as described above. In addition, the system 440 mayfunction in a monopolar mode in which a high frequency voltagedifference is applied between the active electrode(s) 410, and thedispersive return pad 450. In the exemplary embodiment, the pad 450 andthe probe 400 are coupled together, and are both disposable, single-useitems. The pad 450 includes an electrical connector 452 that extendsinto handle 404 of probe 400 for direct connection to the power supply.Of course, the invention would also be operable with a standard returnpad that connects directly to the power supply. In this embodiment, thepower supply 460 will include a switch, e.g., a foot pedal 462, forswitching between the monopolar and bipolar modes. In the bipolar mode,the return path on the power supply is coupled to return electrode 408on probe 400, as described above. In the monopolar mode, the return pathon the power supply is coupled to connector 452 of pad 450, activeelectrode(s) 410 are decoupled from the electrical circuit, and returnelectrode 408 functions as the active electrode This allows the surgeonto switch between bipolar and monopolar modes during, or prior to, thesurgical procedure (discussed in more detail below in conjunction withFIGS. 18-21). In some cases, it may be desirable to operate in themonopolar mode to provide deeper current penetration and, thus, agreater thermal heating of the tissue surrounding the return electrodes.In other cases, such as ablation of tissue, the bipolar modality may bepreferable to limit the current penetration to the tissue.

In one configuration, the dispersive return pad 450 is adapted forcoupling to an external surface of the patient in a region substantiallyclose to the target region. For example, during the treatment of tissuein the head and neck, the dispersive return pad is designed andconstructed for placement in or around the patient's shoulder, upperback or upper chest region. This design limits the current path throughthe patient's body to the head and neck area, which minimizes the damagethat may be generated by unwanted current paths in the patient's body,particularly by limiting current flow through the patient's heart. Thereturn pad is also designed to minimize the current densities at thepad, to thereby minimize patient skin burns in the region where the padis attached.

Referring to FIGS. 15-17, the electrosurgical device according to thepresent invention may also be configured as a catheter system 400. Asshown in FIG. 15, a catheter system 400 generally comprises anelectrosurgical catheter 460 connected to a power supply 28 by aninterconnecting cable 486 for providing high frequency voltage to atarget tissue and an irrigant reservoir or source 600 for providingelectrically conducting fluid to the target site. Catheter 460 generallycomprises an elongate, flexible shaft body 462 including a tissueremoving or ablating region 464 at the distal end of body 462. Theproximal portion of catheter 460 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 460 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 496 is removablyconnected to a distal cable connector 494 which, in turn, is removablyconnectable to generator 28 through connector 492. One or moreelectrically conducting lead wires (not shown) within catheter 460extend between one or more active electrodes 463 at tissue ablatingregion 464 and one or more corresponding electrical terminals (also notshown) in catheter connector 496 via active electrode cable branch 487.Similarly, one or more return electrodes 466 at tissue ablating region464 are coupled to a return electrode cable branch 489 of catheterconnector 496 by lead wires (not shown). Of course, a single cablebranch (not shown) may be used for both active and return electrodes.

Catheter body 462 may include reinforcing fibers or braids (not shown)in the walls of at least the distal ablation region 464 of body 462 toprovide responsive torque control for rotation of electrode terminalsduring tissue engagement. This rigid portion of the catheter body 462preferably extends only about 7 to 10 mm while the remainder of thecatheter body 462 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

Conductive fluid 30 is provided to tissue ablation region 464 ofcatheter 460 via a lumen (not shown in FIG. 15) within catheter 460.Fluid is supplied to lumen from the source along a conductive fluidsupply line 602 and a conduit 603, which is coupled to the innercatheter lumen at multi-lumen fitment 114. The source of conductivefluid (e.g., isotonic saline) may be an irrigant pump system (not shown)or a gravity-driven supply, such as an irrigant reservoir 600 positionedseveral feet above the level of the patient and tissue ablating region8. A control valve 604 may be positioned at the interface of fluidsupply line 602 and conduit 603 to allow manual control of the flow rateof electrically conductive fluid 30. Alternatively, a metering pump orflow regulator may be used to precisely control the flow rate of theconductive fluid.

System 400 further includes an aspiration or vacuum system (not shown)to aspirate liquids and gases from the target site. The aspirationsystem will usually comprise a source of vacuum coupled to fitment 614by a aspiration connector 605.

FIGS. 16 and 17 illustrate the working end 464 of an electrosurgicalcatheter 460 constructed according to the principles of the presentinvention. As shown in FIG. 16, catheter 460 generally includes anelongated shaft 462 which may be flexible or rigid, and an electrodesupport member 620 coupled to the distal end of shaft 462. Electrodesupport member 620 extends from the distal end of shaft 462 (usuallyabout 1 to 20 mm), and provides support for a plurality of electricallyisolated electrode terminals 463. Electrode support member 620 andelectrode terminals 462 are preferably secured to a tubular supportmember 626 within shaft 460 by adhesive 630.

The electrode terminals 463 may be constructed using round, square,rectangular or other shaped conductive metals. By way of example, theelectrode terminal materials may be selected from the group includingstainless steel, tungsten and its alloys, molybdenum and its alloys,titanium and its alloys, nickel-based alloys, as well as platinum andits alloys. Electrode support member 620 is preferably a ceramic, glassor glass/ceramic composition (e.g., aluminum oxide, titanium nitride).Alternatively, electrode support member 620 may include the use ofhigh-temperature biocompatible plastics such as polyether-ether-keytone(PEEK) manufactured by Vitrex International Products, Inc. orpolysulfone manufactured by GE Plastics. The adhesive 630 may, by way ofexample, be an epoxy (e.g., Master Bond EP42HT) or a silicone-basedadhesive.

As shown in FIG. 17B, a total of 7 circular active electrodes orelectrode terminals 463 are shown in a symmetrical pattern having anactive electrode diameter, D₁ in the range from 0.05 mm to 1.5 mm, morepreferably in the range from 0.1 mm to 0.75 mm. The interelectrodespacings, W₁ and W₂ are preferably in the range from 0.1 mm to 1.5 mmand more preferably in the range from 0.2 mm to 0.75 mm. The distancebetween the outer perimeter of the electrode terminal 463 and theperimeter of the electrode support member, W₃ is preferably in the rangefrom 0.1 mm to 1.5 mm and more preferably in the range from 0.2 mm to0.75 mm. The overall diameter, D₂ of the working end 464 of catheterbody 462 is preferably in the range from 0.5 mm to 10 mm and morepreferably in the range from 0.5 mm to 5 mm. As discussed above, theshape of the active electrodes may be round, square, triangular,hexagonal, rectangular, tubular, flat strip and the like and may bearranged in a circularly symmetric pattern or may, by way of example, bearranged in a rectangular pattern, square pattern, or strip.

Catheter body 462 includes a tubular cannula 626 extending along body462 radially outward from support member 620 and electrode terminals463. The material for cannula 626 may be advantageously selected from agroup of electrically conductive metals so that the cannula 626functions as both a structural support member for the array of electrodeterminals 463 as well as a return electrode 624. The support member 626is connected to an electrical lead wire (not shown) at its proximal endwithin a connector housing (not shown) and continues via a suitableconnector to power supply 28 to provide electrical continuity betweenone output pole of high frequency generator 28 and said return electrode624. The cannula 626 may be selected from the group including stainlesssteel, copper-based alloys, titanium or its alloys, and nickel-basedalloys. The thickness of the cannula 626 is preferably in the range from0.08 mm to 1.0 mm and more preferably in the range from 0.1 mm to 0.4mm.

As shown in FIG. 16, cannula 626 is covered with an electricallyinsulating sleeve 608 to protect the patient's body from the electriccurrent. Electrically insulating sleeve 608 may be a coating (e.g.,nylon) or heat shrinkable plastic (e.g., fluoropolymer or polyester).The proximal portion of the cannula 626 is left exposed to function asthe return electrode 624. The length of the return electrode 624, L₅ ispreferably in the range from 1 mm to 30 mm and more preferably in therange from 2 mm to 20 mm. The spacing between the most distal portion ofthe return electrode 624 and the plane of the tissue treatment surface622 of the electrode support member 620, L₁ is preferably in the rangefrom 0.5 mm to 30 mm and more preferably in the range from 1 mm to 20mm. The thickness of the electrically insulating sleeve 608 ispreferably in the range from 0.01 mm to 0.5 mm and more preferably inthe range from 0.02 mm to 0.2 mm.

In the representative embodiment, the fluid path is formed in catheterby an inner lumen 627 or annular gap between the return electrode 624and a second tubular support member 628 within shaft 460. This annulargap may be formed near the perimeter of the shaft 460 as shown in FIG.16 such that the electrically conducting fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 460 (not shown) so that the fluid flows radially outward. Inboth of these embodiments, a fluid source (e.g., a bag of fluid elevatedabove the surgical site or having a pumping device), is coupled tocatheter 460 via a fluid supply tube (not shown) that may or may nothave a controllable valve.

In an alternative embodiment shown in FIG. 17A, the electricallyconducting fluid is delivered from a fluid delivery element (not shown)that is separate from catheter 460. In arthroscopic surgery, forexample, the body cavity will be flooded with isotonic saline and thecatheter 460 will be introduced into this flooded cavity. Electricallyconducting fluid will be continually resupplied to maintain theconduction path between return electrode 624 and electrode terminals463.

Referring to FIGS. 18-21, methods for treating air passage disordersaccording to the present invention will now be described. In theseembodiments, an electrosurgical probe such as one described above can beused to ablate targeted masses including, but not limited to, thetongue, tonsils, turbinates, soft palate tissues (e.g., the uvula), hardtissue and mucosal tissue. In one embodiment, selected portions of thetongue 314 are removed to treat sleep apnea or snoring. In this method,the distal end of an electrosurgical probe 90 is introduced into thepatient's mouth 310, as shown in FIG. 18. If desired, an endoscope (notshown), or other type of viewing device, may also be introduced, orpartially introduced, into the mouth 310 to allow the surgeon to viewthe procedure (the viewing device may be integral with, or separatefrom, the electrosurgical probe). The electrode terminals 104 arepositioned adjacent to or against the back surface 316 of the targetsite, e.g., the tongue 314, and electrically conductive fluid isdelivered to the target site, as described above. Alternatively, theconductive fluid is applied to the target site, or the distal end ofprobe 90 is dipped into conductive fluid or gel prior to introducing theprobe 90 into the patient's mouth. The power supply 28 is then activatedand adjusted such that a high frequency voltage difference is appliedbetween electrode terminals 104 and return electrode 112 in the presenceof the conductive fluid to remove selected portions of the back of thetongue 314, as described above, without damaging sensitive structures,such as nerves, and the bottom portion of the tongue 314.

In the preferred embodiment, the high frequency voltage is sufficient toconvert the electrically conductive fluid (not shown) between the targettissue and electrode terminal(s) 104 into an ionized vapor layer orplasma. As a result of the applied voltage difference between electrodeterminal(s) 140 and the target tissue, charged particles in the plasmaare accelerated towards the occlusion to cause dissociation of themolecular bonds within tissue structures, as discussed above. During theprocess, products of ablation and excess electrically conductive fluid,and other fluids (e.g., blood) may be aspirated from the target site tofacilitate the surgeon's view. During ablation of the tissue, theresidual heat generated by the current flux lines (typically less than150° C.), will usually be sufficient to coagulate any severed bloodvessels at the site. If not, the surgeon may switch the power supply 28into the coagulation mode by lowering the voltage to a level below thethreshold for fluid vaporization, as discussed above. This simultaneoushemostasis results in less bleeding and facilitates the surgeon'sability to perform the procedure. Once the blockage has been removed,aeration and drainage are reestablished to allow the sinuses to heal andreturn to their normal function.

Depending on the procedure, the surgeon may translate the electrodeterminals 104 relative to the target tissue to form holes, channels,stripes, divots, craters or the like within the tongue. In addition, thesurgeon may purposely create some thermal damage within these holes, orchannels to form scar tissue that will stiffen the target tissue, e.g.,the tongue, and minimize air passage blockage after the procedure. Inone embodiment, the physician axially translates the electrode terminals104 into the tongue tissue as the tissue is volumetrically removed toform one or more holes in the turbinate, typically having a diameter ofless than 2 mm, preferably less than 1 mm. In another embodiment, thephysician translates the electrode terminals 104 across the outersurface 316 of the tongue 314 to form one or more channels or troughs.Applicant has found that the present invention can quickly and cleanlycreate such holes, divots or channels in tissue with the cold ablationtechnology described herein. A more complete description of methods forforming holes or channels in tissue can be found in U.S. Pat. No.5,683,366, the complete disclosure of which is incorporated herein byreference for all purposes.

Another advantage of the present invention is the ability to preciselyablate channels or holes within the tissue without causing necrosis orthermal damage to the underlying and surrounding tissues, nerves (e.g.,the optic nerve) or bone. In addition, the voltage can be controlled sothat the energy directed to the target site is insufficient to ablatebone or adipose tissue (which generally has a higher impedance than thetarget sinus tissue). In this manner, the surgeon can literally cleanthe tissue off the bone, without ablating or otherwise effectingsignificant damage to the bone.

FIGS. 19-21 illustrate a specific method for treating obstructive sleepdisorders by treating the back of the patient's tongue 314. In thisprocedure, a plurality of holes or channels 702 are formed in the backof the patient's tongue 314. Holes 702 are preferably formed with themethods described in detail above. Namely, a high frequency voltagedifference is applied between active and return electrodes 362, 360,respectively, in the presence of an electrically conductive fluid. Thefluid may be delivered to the target site, applied directly to thetarget site, or the distal end of the probe may be dipped into the fluidprior to the procedure. The voltage is sufficient to vaporize the fluidaround active electrodes 362 to form a plasma with sufficient energy toeffect molecular dissociation of the tissue. The distal end of the probe350 is then axially advanced through the tissue as the tissue is removedby the plasma in front of the probe 350. As shown in FIGS. 19 and 20,holes 702 will typically have a depth D in the range of about 0.5 to 2.5cm, preferably about 1.2 to 1.8 cm, and a diameter d of about 0.5 to 5mm, preferably about 1.0 to 3.0 mm. The exact diameter will, of course,depend on the diameter of the electrosurgical probe used for theprocedure.

Referring to FIG. 21, during the formation of each hole 702, theconductive fluid between active and return electrodes 362, 360 willgenerally minimize current flow into the surrounding tissue, therebyminimizing thermal damage to the tissue. Therefore, severed bloodvessels in the surface 704 of the hole 702 may not be coagulated as theelectrodes 362 advance through the tissue. In addition, in someprocedures, it may be desired to thermally damage the surface 704 of thehole 702 to stiffen the tissue. Applicant has discovered that stiffeningthe tissue at the back of the tongue 314 reduces air passage obstructionafter the procedure. For these reasons, it may be desired in someprocedures to increase the thermal damage caused to the surface 704 oftongue. In one embodiment, the physician switches the electrosurgicalsystem from the ablation mode to the subablation or thermal heating modeafter the hole 702 has been formed. This is typically accomplished bypressing a switch or foot pedal to reduce the voltage applied to a levelbelow the threshold required for ablation for the particular electrodeconfiguration and the conductive fluid being used in the procedure (asdescribed above). In the subablation mode, the physician will thenremove the distal end of the probe 350 from the hole 702. As the probeis withdrawn, high frequency current flows from the active electrodes362 through the surrounding tissue to the return electrode 360. Thiscurrent flow heats the tissue and coagulates severed blood vessels atsurface 704.

In some embodiments, it may be desired to increase the thermal damage ofsurface 704 to create scar tissue around the hole. In these embodiments,it may be necessary to either: (1) withdraw the probe 350 slowly, e.g.,about 0.5 to 1.0 cm/sec; or (2) hold the probe 350 within the hole 702for a period of time, e.g., on the order of 1 to 30 seconds, while inthe subablation mode. The current flows through the tissue surroundinghole 702 during this time period and creates thermal damage therein. Inthe representative embodiment, the thermal necrosis 706 will extendabout 1.0 to 5.0 mm from surface 704 of hole 702. In this embodiment,the probe may include one or more temperature sensors (not shown) onprobe coupled to one or more temperature displays on the power supply 28such that the physician is aware of the temperature within the hole 702during the procedure.

In addition to the above procedures, the system and method of thepresent invention may be used for treating a variety of disorders in themouth 310, pharynx 330, larynx 335, hypopharynx, trachea 340, esophagus350 and the neck 360 (see FIG. 18). For example, tonsillar hyperplasisor other tonsil disorders may be treated with a tonsillectomy bypartially ablating the lymphoepithelial tissue. This procedure isusually carried out under intubation anesthesia with the head extended.An incision is made in the anterior faucial pillar, and the connectivetissue layer between the tonsillar parenchyma and the pharyngealconstrictor muscles is demonstrated. The incision may be made withconventional scalpels, or with the electrosurgical probe of the presentinvention. The tonsil is then freed by ablating through the upper poleto the base of the tongue, preserving the faucial pillars. The probeablates the tissue, while providing simultaneous hemostasis of severedblood vessels in the region. Similarly, adenoid hyperplasis, or nasalobstruction leading to mouth breathing difficulty, can be treated in anadenoidectomy by separating (e.g., resecting or ablating) the adenoidfrom the base of the nasopharynx.

Other pharyngeal disorders can be treated according to the presentinvention. For example, hypopharyngeal diverticulum involves smallpouches that form within the esophagus immediately above the esophagealopening. The sac of the pouch may be removed endoscopically according tothe present invention by introducing a rigid esophagoscope, andisolating the sac of the pouch. The cricopharyngeus muscle is thendivided, and the pouch is ablated according to the present invention.Tumors within the mouth and pharynx, such as hemangionmas,lymphangiomas, papillomas, lingual thyroid tumors, or malignant tumors,may also be removed according to the present invention.

Other procedures of the present invention include removal of vocal cordpolyps and lesions and partial or total laryngectomies. In the latterprocedure, the entire larynx is removed from the base of the tongue tothe trachea, if necessary with removal of parts of the tongue, thepharynx, the trachea and the thyroid gland.

Tracheal stenosis may also be treated according to the presentinvention. Acute and chronic stenoses within the wall of the trachea maycause coughing, cyanosis and choking.

What is claimed is:
 1. A method for treating obstructive sleep disorderscomprising:positioning an active electrode adjacent to a tissuestructure in a patient's mouth or throat; applying high frequencyvoltage between the active electrode and a return electrode, the highfrequency voltage being sufficient to ablate tissue; during the applyingstep, advancing the active electrode into the tissue to generate a spacewithin the tissue; and removing the active electrode from the spacewithin the tissue.
 2. The method of claim 1 further comprising, duringthe removing step, applying high frequency voltage between the activeand return electrodes, the high frequency voltage being sufficient tocoagulate blood at the tissue surface surrounding the space.
 3. Themethod of claim 2 wherein the high frequency voltage during the removalstep is sufficient to thermally damage the surface of the tissuesurrounding the space.
 4. The method of claim 1 further comprisingproviding an electrically conductive fluid around the active electrodeand between the active and return electrodes prior to the applying step.5. The method of claim 4 wherein the providing step comprisespositioning the active and return electrodes within a source ofelectrically conductive fluid and then positioning the active and returnelectrodes into the patient's mouth adjacent to the tissue structure. 6.The method of claim 4 wherein the providing step comprises deliveringthe electrically conductive fluid to the active and return electrodes atthe target site in the patient's mouth.
 7. The method of claim 4 furthercomprising generating a current flow path between the active and returnelectrodes with the electrically conductive fluid.
 8. The method ofclaim 4 further comprising aspirating fluid from a region around theactive electrode.
 9. The method of claim 4 wherein the electricallyconductive fluid is not present during the removal step.
 10. The methodof claim 1 further comprising applying a sufficient high frequencyvoltage difference between the active and return electrodes to effectmolecular dissociation of at least a portion of the tissue structureduring the advancing step.
 11. The method of claim 1 wherein theapplying step includes generating a voltage gradient between the activeand return electrodes, the voltage gradient being sufficient to createan electric field that breaks down the tissue through moleculardissociation.
 12. The method of claim 1 wherein the positioning step iscarried out by positioning a single, active electrode adjacent to thetissue structure.
 13. The method of claim 1 wherein the positioning stepis carried out by positioning a plurality of electrically isolatedelectrode terminals adjacent to the tissue structure.
 14. The method ofclaim 1 further comprising applying sufficient voltage to the activeelectrode in the presence of electrically conducting fluid to vaporizeat least a portion of the fluid between the active electrode and thetissue structure.
 15. The method of claim 14 further comprisingaccelerating charged particles from the vaporized fluid to the tissue tocause dissociation of the molecular bonds within the tissue structures.16. The method of claim 1 further comprising axially translating theactive electrode to form a hole through at least a portion of the tissuestructure.
 17. The method of claim 1 further comprising transverselytranslating the active electrode relative to the tissue structure toform a channel along the outer surface of the tissue structure.
 18. Themethod of claim 1 wherein the space has a maximum lateral dimension lessthan about 2 mm.
 19. The method of claim 1 wherein the space has amaximum lateral dimension less than about 1 mm.
 20. The method of claim1 wherein the positioning step is carried out by providing an electrodeand a return electrode on a distal portion of a shaft of anelectrosurgical instrument and positioning the distal portion of theshaft adjacent to the tissue structure.
 21. The method of claim 20wherein the return electrode is axially spaced at least about 1.0 mmfrom the active electrode.
 22. The method of claim 20 furthercomprising, during the removal step, deactivating the active electrodeand applying a high frequency voltage difference between a second activeelectrode and one or more return electrodes on the instrument shaft. 23.The method of claim 22 wherein the second active electrode is spacedproximally from the return electrode.
 24. The method of claim 23 whereinthe instrument shaft comprises a second return electrode spacedproximally from the second active electrode, the method comprising,during the removal step, applying a high frequency voltage differencebetween the second active electrode and the first and second returnelectrodes.
 25. The method of claim 20 further comprising, during theremoval step, deactivating the active electrode and applying a highfrequency voltage difference between the return electrode on theinstrument shaft and a dispersive return electrode coupled to anexternal surface of the patient.